decreasing equalizer-10bands band0(29 Hz) boosts a 60 Hz test signal

decreasing equalizer-10bands band0(29 Hz) boosts a 60 Hz test signal

Hi

I am using the 10 bands equalizer in my application https://github.com/wwmm/pulseeffects and I noticed a behavior that seems strange to me. When I send a 59 Hz test signal to the equalizer its amplitude increases when I decrease band0 level. Is this the expected behavior? I could reproduce this with the following commands:

I can hear a louder sound with the second command. I thought that the shelf filter at 29 Hz would not affect higher frequencies. When the test signal has a frequency of 29 Hz the sound amplitude decreases with band0 level as I would expect. So it has something to do with the overlap between band0 and band1.